The western rat snake (Pantherophis obsoletus), also commonly known as the Texas ratsnake,[3]black rat snake, pilot black snake, or simply black snake.[4] is a nonvenomous species of Colubridae found in central North America. No subspecies are currently recognized.[5]

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Rat snakes are found from New England south through Florida and west through the eastern half of Texas and Nebraska and north again to southern Wisconsin. The black rat snake is the most widely distributed common rat snake with a range from New England south through Georgia and west across the northern parts of Alabama, Mississippi, and Louisiana, and north through Oklahoma to southern Wisconsin. There is also an isolated population in southern Canada and northern New York. The yellow rat snake is found along the coast of the Carolinas south through Georgia and Florida. The Everglades rat snake has an isolated population in southern Florida's Everglades. The gray rat snake ranges from southern Georgia and northern Florida west through Mississippi and north to southern Kentucky. The Texas rat snake can be found in southern Oklahoma, Texas, and Louisiana. Common rat snakes live in a variety of habitats with each subspecies preferring a slightly different one. Some of these habitats overlap with one another. Common rat snakes are excellent climbers and spend a lot of time in trees. Black rat snakes live at elevations from sea level to high altitudes in the Appalachian Mountains. Black rat snakes live in habitats ranging from a rocky hillside to flat farmland.[6]

It prefers heavily wooded areas and is known for having excellent climbing ability, including the ability to climb the trunk of large mature trees without the aid of branches. This snake is a competent swimmer. During winter it hibernates in dens, often with copperheads and timber rattlesnakes. This association gave rise to one of its common names, pilot black snake, and the superstition that this nonvenomous species led the venomous ones to the den.

Adults can become quite large, with a reported typical length of 106.5–183 cm (3 ft 6 in–6 ft 0 in).[7][8] They are the largest snake found in Canada. The record total length is 256.5 cm (8 ft 5 in),[9] making it (officially) the longest snake in North America.[8] Unofficially, indigo snakes (Drymarchon couperi) are known to exceed them, and one wild-caught pine snake (Pituophis melanoleucus), with a portion of its tail missing, measured 111 inches (2.8 m).[citation needed] The body mass of this rat snake is commonly 0.5 to 2.2 kg (1.1 to 4.9 lb) in large adults.[10][11]

Juveniles are strongly patterned with brown blotches on a gray background (like miniature fox snakes, Pantherophis gloydi and Pantherophis vulpinus). Darkening occurs rapidly as they grow. Adults are glossy black above with white lips, chin, and throat. Sometimes traces of the "obsolete" juvenile pattern are still discernible in the skin between the scales, especially when stretched after a heavy meal.[12][13]

When not fully grown, rat snakes are subject to predation by many animals, including other snakes. Once they attain maturity, they are readily preyed on by humans, as well as mammalian carnivores (including the American mink, which weighs no more than an adult rat snake) and large birds of prey (especially red-tailed hawks).[15] When startled, they may freeze and wrinkle themselves into a series of kinks. If they feel further threatened, they may flee quickly or vibrate their tails in dead leaves (a form of mimicry, which makes them sound like rattlesnakes). They are also capable of producing a foul-smelling musk, which they will release onto predators if picked up. They spread the musk with their tails in hopes of deterring the threat.[16] When cornered or provoked, black snakes are known to stand their ground and can become aggressive. Counterattacks on large birds of prey, often committed by large snakes in excess of 150 cm (59 in) in length, have resulted in violent prolonged struggles. Utilizing its infamous agility and the great strength of its muscular coils, the black rat snake is sometimes able to overwhelm and kill formidable avian predators such as Red-tailed Hawks, Great Horned Owls and Red-shouldered Hawks, though in many cases the bird is able to kill the snake and both combatants may even die.[17][18]

This species is a constrictor, meaning it suffocates its prey, coiling around small animals and tightening its grip until they can no longer draw breath, before eating them. Though they will often consume mice, voles, and rats, western rat snakes are far from specialists at this kind of prey and will readily consume any small vertebrate they can catch. Other prey opportunistically eaten by this species can include other snakes (including both those of their own and other species), frogs, lizards, chipmunks, squirrels, juvenile rabbits, juvenile opossums, songbirds, and bird eggs.[12] One snake was observed to consume an entire clutch of mallard eggs.[15] Cavity-nesting bird species are seemingly especially prevalent in this snake's diet. The rat snake has been noted as perhaps the top predator at purple martin colonies as a single large snake will readily consume a number of eggs, hatchlings, and adults each summer. Several rat snake repelling methods have been offered to those putting up martin houses, but most are mixed in success.[19]

Mating takes place in late May and early June. The male snake wraps its tail around the female with their vents nearly touching. The male then everts one of its sex organs, a hemipenis, into the female sex organ, cloaca. The mating lasts a few minutes to a few hours. After five weeks, the female lays about 12 to 20 eggs, which are 36–60 mm (1.4-2 in.) long by 20–26.5 mm (0.8–1.1 in.) wide. The eggs hatch about 65 to 70 days later in late August to early October.[20] The hatchlings are 28–41 cm (11–16 in.) in total length,[14] and they look like miniature fox snakes.[12]

This species has previously been placed (and is still placed by many) in the genus Elaphe, as Elaphe obsoleta. However, Utiger et al. found that Elaphe is broadly construed as paraphyletic, and placed this species in the genus Pantherophis.[21] In addition, because Pantherophis is masculine, the specific epithet becomes the masculine obsoletus.[22] The split of Pantherophis from Elaphe has been further confirmed by additional phylogenetic studies.[23][24]

In 2001, Burbrink suggested this species be divided into three species based on geographic patterns of mitochondrial DNA diversity. He assigned new common names and resurrected old scientific names, resulting in the following combinations: eastern ratsnake (Elaphe alleghaniensis, now Pantherophis alleghaniensis), central ratsnake (Elaphe spiloides, now Pantherophis spiloides), and westen rat snake (Elaphe obsoleta, now Pantherophis obsoletus). However, these three species are not morphologically distinct and overlap in all examined morphological characters.[25] More recent investigations have indicated P. alleghaniensis and P. spiloides interbreed freely in Ontario.[26]

In 2008, Collins and Taggart[27] resurrected the genus Scotophis for Burbrink's three taxa, i.e., (Scotophis alleghaniensis), (Scotophis spiloides) and (Scotophis obsoletus) in response to the findings of Burbrink and Lawson, 2007.[23] The justification for this nomenclatural change has been removed by more recent research.[24]

Western rat snakes are popular as pets. Their size, calm temperament, and ease of care contribute to this popularity and they also come in many mutations such as leucistic, albino and scaleless. They enjoy hiding and burrowing which is usually accommodated with a loose substrate (such as aspen wood shavings or newspaper) and one or more hide boxes. Captive rat snakes are generally fed pre-killed or stunned mice because captive-bred mice reduce the risk of exposing the snake to pathogens or live prey-induced injuries.

Say, T.InJames, E. (1823). Account of an Expedition from Pittsburgh to the Rocky Mountains, Performed in the Years 1819 and '20, by Order of the Hon. J.C. Calhoun, Sec'y of War: Under the Command of Major Stephen H. Long. From the Notes of Major Long, Mr. T. Say, and other Gentlemen of the Exploring Party. Vol. I. Philadelphia: H.C. Carey and I. Lea. 503 pp. (Coluber obsoletus, p. 140).